Direct drive led driver and offline charge pump and method therefor

ABSTRACT

In one embodiment, a Light Emitting Diode (LED) driving device for driving a plurality of LEDs has a switching matrix utilizing a plurality of one of a turn off thyristors or turn off triacs coupled to the plurality of LEDs. A controller is coupled to the switching matrix responsive to a voltage of a rectified AC halfwave, wherein combinations of the plurality of LEDs are altered to ensure a maximum operating voltage of the plurality of LEDs is not exceeded. A current limiting device is coupled to the combinations of the plurality of LED to regulate current. 
     In a second embodiment an offline charge pump utilizes a switching matrix to recombine capacitors in accordance with the voltage on the AC half wave and then in accordance with a desired output voltage to feed a load, such that said recombinations occur at a frequency much higher than the frequency of the AC rectified half wave such that charge is “pumped” from the input at one voltage to the output at another voltage through the AC halfwave while providing a constant output voltage to the load.

RELATED APPLICATIONS

This application is related to U.S. Provisional Application Ser. No.61/665,864, filed Jun. 28, 2012, in the name of the same inventor listedabove, and entitled, “DIRECT DRIVE LED DRIVER & OFFLINE CHARGE PUMP”,the present patent application claims the benefit under 35 U.S.C.§119(e).

TECHNICAL FIELD

This application generally relates to a Light Emitting Diode (LED)driver, and more particularly, to an improved direct drive LED driverand in an alternative embodiment to an offline charge pump capable ofcreating a constant output voltage to drive LEDs or other loadsrequiring a constant output voltage.

BACKGROUND

Direct drive schemes have been popular recently to power solid statelighting, such as Light Emitting Diode (LED) light bulbs, to avoid thecost or complexity of switching regulators which bring with themunwanted EMI filter and bill of material expenses. Various direct driveschemes have been suggested, however, they generally include utilizingseveral subsets of one or more series connected LEDs which are shortedor bypassed by switches to increase or decrease the total forwardvoltage in proportion to the AC input. Normally the switches used areMOSFETs which are turned on or off depending upon the AC input voltageat the time.

To improve power factor and reduce total harmonic distortion (THD),these types of switching schemes are used in conjunction with valleyfill power factor correction schemes (VFPFC). These schemes break up theinput capacitor into two or more capacitors to alter the effective inputand discharge capacitance so as to distribute the input conduction angleover a wider range and spread the capacitance discharge over a widerconduction angle.

Unfortunately, these schemes underutilize expensive LEDs because many ofthem are only on for a portion of the conduction cycle rather thancontinuously as with more expensive switching regulator based schemes.Additionally, these schemes are not useful for voltage mode applicationssuch as cell phone or portable equipment chargers which require aconstant average output voltage.

Standard wall dimmers create phase control type dimming that isdifficult to correlate with direct drive schemes since direct driverequires a continuous half wave rectified signal to make good use of theLEDs. Valley fill Power Factor Correction (PFC) schemes are poorlycompatible with these types of schemes since they are generally passiveor minimally active and not responsive to phase control type signals.Most direct drive schemes working with phase control dimmers will turnon only a small fraction of the available LEDs leaving much of aluminaire unilluminated. The eye is generally dissatisfied with theresulting bright spot in the luminaire rather than a continuous dimmingacross all of the LEDs in the physical LED array.

The basic limitation on improving the utilization of LEDs, or allowingmore complex offline capacitor schemes is the cost of the switches.MOSFETs are expensive especially at high voltage and therefore muchemphasis is placed on reducing the voltage on each MOSFET and inaddition reducing the number of switches. This results in a number ofproblems including flicker, poor total harmonic distortion (THD), EMI,poor LED utilization & reduced power factor. More switches would reduceflicker, allow better power factor, improve total harmonic distortion(THD) & LED utilization, and reduce use of capacitors. Therefore, itwould be desirable to have a mechanism that maximizes the conductiontime of all LEDs. It would be especially desirable if it were alsocompatible with phase control dimming.

Alternatively, a mechanism compatible with a fixed voltage output byconnecting capacitors groups in conformance with the rectified AC inputvoltage which switches said capacitors at frequencies much higher thanthe input sine wave frequency, from a series-parallel arrangementcompatible with the instantaneous input voltage, to a series-parallelconfiguration compatible with an output or load voltage, would bedesirable. Such an offline charge pump configuration compatible withportable equipment such as power supply or charger circuits also knownas “wall warts,” common for cell phones, tablets or laptop computers,could greatly reduce the cost, size, component count, weight andovercome EMI disadvantages of existing circuits.

It would be desirable to have a switching matrix with superiorproperties to MOSFETs, bipolar transistors or even insulated gatebipolar transistors (IGBTs) such that more complex switching matrix forLEDs or capacitors might be utilized at reasonable cost, The bestdevices in terms of current density (see FIG. 9) are thyristors. Thesethyristors, however, must be capable of turning on and off withoutrelying on the current to fall to zero as in normal thyristor circuits.This is accomplished utilizing Gate Turn Off (GTO) thyristors and/or MosControlled Thyristors (MCT) which can be turned off in response to acontrol signal.

Commercially available GTO and thyristors are only available inindividual vertical form and generally only at high current levels.Additionally, no arrays or groups of turn off thyristors on the samesilicon substrate which are isolated relative to one another have beendemonstrated. The use of turn off thyristors for offline voltage modeapplications requires such isolated devices as creating a substrate orpackage capable of dealing with multiple potentials is too expensive foroffline LED drivers or power supplies. It would therefore be desirableto have a switch matrix based on turn off thyristors such asGTOs/MCTs/turn off TRIACs that can be made on a single piece of siliconas a switching array at low cost.

Finally, it would be desirable to have a scheme for level shifting thecontrol signals that drive the control nodes of said turn off thyristorsindividually or in combinations of two in reverse parallel configuration(turn off TRIACs) such that the voltage and current limits on saidcontrol nodes are maintained (i.e. Safe Operating Area (SOA)) whilesimultaneously eliminating the need for high valued resistor basedschemes with long time constants which reduce the number of times percycle that switching can occur.

Therefore, a need exists to provide a device and method to overcome theabove problems.

SUMMARY OF THE INVENTION

A Light Emitting Diode (LED) driving device for driving a plurality ofLEDs has a switching matrix utilizing a plurality of one or more of aturn off thyristors or turn off triacs coupled to the plurality of LEDs.A controller is coupled to the switching matrix responsive to a voltageof a rectified AC halfwave, wherein combinations of the plurality ofLEDs are altered to ensure a maximum operating voltage of the pluralityof LEDs is not exceeded. A current limiting device is coupled to thecombinations of the plurality LED to regulate current.

An offline charge pump device has a switched capacitor array having aplurality of capacitors using one or more of turn off thyristors orparallel reverse combinations as switches to create a turn off TRIACconnecting at least two of the plurality of capacitors. A controllerdevice operating at a frequency higher than an AC rectified half wave iscoupled to the switched capacitor array responsive to a voltage of therectified AC half wave. The controller device forms capacitorcombinations from the plurality of capacitors such that the capacitorcombinations do not exceed their individual maximum voltage ratingsduring a first part of a frequency cycle. The controller devicerearranges the capacitor combination resulting in a desired outputvoltage during a second part of the frequency cycle (said frequencycycle much higher than the rectified AC half wave frequency). A couplingdevice is used for connecting the plurality of capacitors by the turnoff thyristors to the voltage of the AC half wave during the first partof the frequency cycle and then to an output during the second part ofthe frequency cycle.

A capacitor device may be multiple individual capacitors or a singlecapacitor with a plurality of accessible plate members. The plurality ofplate members are separately segmented out to create a seriescombination of capacitors, wherein each capacitor has a lower voltagetolerance than across the entire series combination.

A vertical thyristor array has a plurality of one or more of a MCT orGTO thyristors. The plurality of one or more of a MCT or GTO thyristorsare formed on a common substrate, with one of a common anode or cathodeconnected to the common substrate, for all plurality of one of a MCT orGTO thyristors in the array.

The features, functions, and advantages may be achieved independently invarious embodiments of the disclosure or may be combined in yet otherembodiments.

BRIEF DESCRIPTION OF DRAWINGS

The novel features believed to be characteristic of the application areset forth in the appended claims. In the descriptions that follow, likeparts are marked throughout the specification and drawings with the samenumerals, respectively. The drawing figures are not necessarily drawn toscale and certain figures can be shown in exaggerated or generalizedform in the interest of clarity and conciseness. The application itself,however, as well as a preferred mode of use, further objectives andadvantages thereof, will be best understood by reference to thefollowing detailed description of illustrative embodiments when read inconjunction with the accompanying drawings, wherein:

FIG. 1 is a simplified schematic of a switching matrix of the presentinvention;

FIG. 1A shows one example of the LED connection using the switchingmatrix of FIG. 1;

FIG. 1B shows another example of the LED connection using the switchingmatrix of FIG. 1;

FIG. 1C shows another example of the LED connection using the switchingmatrix of FIG. 1;

FIG. 1D shows another example of the LED connection using the switchingmatrix of FIG. 1;

FIGS. 2A and 2B shows different schematic implementations of anembodiment of the switching matrix wherein the switches are connected toa single supply shorting unused LEDs to maintain a forward voltage inconformance with the input AC halfwave voltage;

FIG. 2C-2H show different configurations of the switching matrix shownin FIG. 2A-2B wherein switches are opened and or closed;

FIG. 21 shows a servo driven transconductor for use in the switchingmatrix of FIG. 2A or 2B;

FIG. 3 shows a switching matrix using a valley fill PFC circuit;

FIG. 3A shows an operation operating waveforms of the switching matrixof FIG. 3;

FIG. 3B shows how the capacitors may be rearranged in a parallelcombination to utilize multiple capacitors to store charge to keep thesystem powered during low dimming levels of phase control dimming fromt₁-t₂;

FIG. 4A shows a novel capacitor construction for the capacitors of theprevious embodiments;

FIG. 4B shows a simplified schematic of the novel capacitor constructionas shown in FIG. 4A;

FIG. 5 shows the capacitor construction for use in an offline capacitorconfiguration;

FIG. 6 shows the capacitors of FIG. 3 connected in parallel during partof the cycle indicated by t₁ which will then be connected in a series orseries parallel combination to an output capacitor and/or load duringanother portion of the cycle, then an arbitrary voltage may be createdby pumping from any part of the AC input line to a desired outputvoltage.

FIG. 7 shows the cross section of the vertical MOS controlled thyristor.

FIG. 7A is a magnified view showing a vertical sinker that can be usedto convert the vertical structure with backside Anode to a device whoseanode can be accessed from the top of the wafer as the other terminalsare.

FIG. 7B shows a top half view of how the figure in 7A may be reflectedsymmetrically around a center point.

FIG. 7C shows an MCT equivalent circuit;

FIG. 7D show how sub-MCT turn off thyristor type sub-cells may beisolated with their Anode connection being brought up to the top sidewith a sinker.

FIG. 8 shows a driver for the MCT, GTO or linear/controlled turn offtype devices;

FIG. 8A illustrates the concept of a turn off TRIAC utilizing gated turnoff thyristors to control a bidirectional current;

FIG. 9 illustrates how MCTs have a higher current density;

FIG. 10 illustrates operation of the offline charge pump wherecapacitors are arrayed in conformance with the rectified AC inputvoltage such that they may transition from an all series to all parallelcombination, or a pattern of series-parallel to series-parallelcombination so as to charge while maintaining a voltage across thecapacitor which will not damage them and then rearranging to create anoutput voltage at a desired magnitude;

FIG. 11 illustrates some applications in which an offline charge pumpmight be used and the advantages that would accrue.

DESCRIPTION OF THE APPLICATION

The description set forth below in connection with the appended drawingsis intended as a description of presently-preferred embodiments of theapplication and is not intended to represent the only forms in which thepresent application can be constructed and/or utilized. The descriptionsets forth the functions and the sequence of steps for constructing andoperating the application in connection with the illustratedembodiments. It is to be understood, however, that the same orequivalent functions and sequences can be accomplished by differentembodiments that are also intended to be encompassed within the spiritand scope of this application.

The invention utilizes turn off thyristors such as gate turn offthyristors (GTO) and/or Mos Controlled Thyristors (MCT) technology tolower the cost of switching and allow reverse blocking. Generally GTOsare known to have a current controlled control node and MCTs to have avoltage controlled control node. FIG. 9 illustrates the advantages ofthese types of switches (which have not been used for direct drive oroffline charge pumps schemes before) over MOSFETs. FIG. 9 illustratesthat MCTs have a higher current density which translates into lesssilicon. This differs from convention direct drive means which generallyutilize external MOSFETs to short groups of LEDs during differentsegments of AC waveform. Simply utilizing these types of devices,however, may not be enough as it may be necessary to combine them on asingle substrate while simultaneously isolating to make them useful.Isolated arrays of these types of thyristors have not been taughtbefore.

The invention may utilize capacitors, preferably a single capacitor withmultiple plates bonded out for use in the switching circuits, althoughmultiple capacitors can also be used. The thickness between differentplates may be altered to optimize the energy stored for differentcapacitor segments or may be of identical thickness but group differentnumbers of plates to store different quantities of energy. It may beuseful to stagger the capacitance and turn on different size capacitorsduring various parts of the AC waveform. Alternatively groups ofcapacitors may be used. The scheme utilizes lower voltage capacitors ineither scheme therefore the voltage across the capacitors must becompatible with the input voltage through the switching pattern. Thislower voltage allows a conventional high voltage capacitor with multipleplates to be utilized simply by having access to the plates as long asthe thickness (voltage) requirements are met at all times. In thisscenario no additional capacitance and size or cost would be requiredbeyond simply pinning out the plates independently.

The invention may utilize a turn off thyristor switching array toconnect groups of LEDs in series, in groups of parallel LEDs in seriesor all LED in series. Turn off thyristors have not been used for thistype of switching, however, they provide a cost effective way to do soversus MOSFETs which are expensive for offline switching and must bepaired in DGD configuration to allow reverse blocking making them evenmore so.

The capacitor switching regimen may be done in two different ways. Thefirst is an offline charge pump where the equivalent capacitors aregrouped according to the input waveform. When the voltage is very lowthey are all in parallel but are regrouped in series to charge up anoutput capacitor and power a load. When the voltage is very high theycan all be in series and then switched into parallel combinations tomatch the desired output voltage. This scheme has the advantage ofminimizing the quantity of switching required on the LEDs or other typesof constant voltage loads since the output voltage may be maintainedthrough the AC half cycle. FIG. 10 demonstrates the scheme graphically.

This scheme has the additional advantage of being compatible withvoltage mode systems such that any input voltage may at first beconnected in such a way as to be compatible with the input voltage andthen rearranged so as to charge an output capacitor and feed a loadwhich requires a different output voltage. The downside of thisarrangement is that it must be switched regularly such that the outputcapacitor and/or load may be kept charged to keep its size reasonable,at a frequency much higher than the AC rectified switching frequency.

In the alternative embodiment turn off thyristors are utilized toconnect LEDs such that they may be used continuously in conjunction withvalley fill PFC. In this case, however, the passive diodes used in atypical valley fill PFC scheme are replaced with turn off thyristorssuch that the valley fill PFC scheme may be accelerated to parallel thefull input capacitance if phase control dimming is detected. This allowsmuch more energy to be stored during the on time of the phase controldimming, especially extremely small phase angles, so that the system maybe kept active.

In addition the valley fill PFC minimum level may be adjusted bychoosing which groups of capacitor plates or which capacitors toutilize. This reduces the amount of capacitance required as smallerminimum voltages may be used in conjunction with the output switcharray.

The numbers of switches required to implement these types of schemes aremuch larger than those typically used for direct drive or valley PFCschemes and have been uneconomical utilizing MOSFET technology. Turn offthyristors allow creation of much larger number of switches at muchlower costs due to their unique structure which has a much highercurrent density than other devices (see FIG. 9), however, in the pastthey were still impractical because their vertical structures requiredisolated substrates which in turn demanded expensive hybrid assembliesincompatible with the very low cost expectations of offline LED driversor power supplies.

To create a cost effective switch matrix it is necessary to create theswitches on a common substrate. To do this two novel methods areintroduced. The first method creates a group of switches with a commonnode. This is compatible with the LED driving scheme for example of FIG.2 where n or p type turn off thyristors may be used to short acrossgroups of LEDs to allow forward voltages for the remaining LEDscompatible with the input voltage. As the input voltage rises soadditional LEDs are “freed” to increase the forward voltage. Even withthis scheme additional current limiting means are anticipated whichmight be as simple as a resistor, or use of a linearly controllable turnoff thyristor, or may include an additional servo driven transconductor(as shown in FIG. 2 b).

The second method utilizes turn off thyristors with a vertical sinkerand buried layer to allow a vertical device with all terminals picked upon one side of the wafer. FIG. 7C illustrates an equivalent latchstructure for an MCT. Using vertical sinkers with multiple MCTs on asingle substrate, while still utilizing the bulk operation of the devicefor current density improvement allows complete isolation of each turnoff thyristor or thyristor subcell. An example is shown in FIG. 7. FIGS.7A and 7D show the sinker made up of isodown and isoup to pick-up the pburied layer in FIG. 7. This structure may be modified by those skilledin the art but a vertical sinker arrangement to pick up a vertical turnoff thyristor structure has not been taught in the past. In the bottomright hand corner of FIG. 7D p+ may be extended for subcells within agiven isolated MCT and then the subcells to the left repeated (withoutthe left side terminator for inner cells and with for the end cells) ora dielectric or wide n region may extend through to the bottom of thewafer to isolate MCTs on the same substrate.

FIG. 7B shows how the construction could be rotated to produce cellswhich combine to form an overall power device, while Figure and 7D alsoshows how sub-MCT turn off thyristor type sub-cells may be isolated withthe anode brought to the same side of the wafer as the cathodes. Thesemay be turned off using a controller in conformance with an input signalsuch as the voltage on the gate, or a timed response, or other mechanismto create a linear thyristor which can control the rate of turn on orturn off of the overall turn off thyristor. Such a linear MCT or GTOwould be very attractive as the result would have the current handlingproperties of MOSFETs, IGBTs or Bipolars such that the turn on and turnoff time can be modulated so as not to produce excessive ringing orother artifacts.

In addition to the turn off thyristor structures, it is necessary tocreate optimized drivers that switch quickly while also utilizing thesmallest possible drive devices possible. FIG. 8 shows such a driverarrangement. Parallel driver arrangements might be utilized and sized soas to stagger the turn off of different subcells to control the turn onand turn off transitions conforming to a control signal such as the MCTgate voltage. Coupling capacitors make this driver capable of driving aGTO current trigger device where the current is determined by acombination of capacitor size, level shifter driver device sizes andpotentially some low side gate slewing circuitry. FIG. 8 a shows a turnoff TRIAC arrangement which could be driven by such drivers eachconforming to its specific type of thyristor topology (p or n), notethat the driver must be referenced to the emitter of the MCT (n beingpulled above and p pulled below).

Referring now to FIGS. 1-5, detailed embodiments of the presentinvention will be disclosed. In all of the figures current is limited byeither a servo controlled current source (transconductor), a thyristoroperating linearly as taught in this application or utilizing a resistoror other passive. Said transconductor may be easily implemented by anoperation amplifier, a bipolar transistor or low voltage MOSFET(protected by thyristor switches), and a resistor with the resistor innegative feedback against a reference voltage as shown in FIG. 2 b.

Referring to FIG. 1, a switch matrix 10 is shown. The switch matrix 10may be used to connect one or more Light Emitting Diodes (LEDs) 12 in aplurality of different configurations. While the present embodimentshows six LEDs, additional or fewer LEDs 12 may be used. The switchingmatrix 10 utilizes a plurality of switches G1-G15 to connect the LightEmitting Diodes (LEDs) 12 in different configurations. The switchingmatrix 10 may utilize turn off thyristors such as Gate Turn Off (GTO) orMos-Controlled Thyristor (MCT) transistors for the switches G1-G15 (orcombinations thereof in on/off triac form). By opening/closing theswitches G1-G15, the switching matrix 10 may be used to create fullparallel groups of one or more high brightness LEDs 12 as shown in FIG.1A. Alternatively groups of parallel combinations of LEDs 12 may beutilized as shown in FIG. 1B and FIG. 1C. The LEDs 12 may also be placedin series as illustrated in FIG. 1D. Those skilled in the art will beable to extend or reduce the combinations as desired to optimizeutilization of LEDs 12, reduce flicker and maximize conduction angle.

Referring now to FIGS. 2A-2B, an embodiment of the switching matrix 20is shown to drive one or more LEDs 12 (See FIGS. 2C-2H). In theswitching matrix 20, the switches 14 are connected to a single supply.As in the previous embodiment, the switching matrix 20 may utilize turnoff thyristors such as Gate Turn Off (GTO) or Mos-Controlled Thyristor(MCT) thyristors for the switches 14 (or combinations thereof in on/offtriac form). In one embodiment the supply to the switches 14 is GND orthe lowest circuit potential, in the other it is V1 or the highestpotential. When the AC voltage is low a single LED 12 is connectedacross the input voltage. As the voltage rises a second switch 14 turnson while the first turns off connecting two LEDs 12 to ground, while thefirst turns on allowing two switches in series. This process continuesuntil all of the LEDs 12 are connected in series across the inputvoltage in conformance with the AC half wave and then the processreverses as the rectified AC half wave falls back towards zero.

In the embodiment shown in FIGS. 2A-2B, additional current limitingmeans may be anticipated which might be as simple as a resistor, or useof a linearly controllable turn off thyristor, or may include anadditional servo driven transconductor. Referring to FIG. 21, atransconductor 22 may be inserted in the switching matrix 20. Thetransconductor 22 may be implemented by using an operation amplifier 24,a lower voltage transistor 26 and a resistor 28 with the resistor 28 innegative feedback against a reference voltage Vr. The transistor 26 maybe a bipolar transistor or MOSFET. The transconductor 22 utilizing thelower voltage transistor 26 and relying on the MCTs and GTOs (switches14) to hold off the voltage. In this case the ground connections shownwould instead be the connection A of the transconductor 22. Thisinstantiation may also be utilized by a purely passive valley fill PFCwithout switches if desired, using any of the common variants known tothose skilled in the art from a single capacitor to multiple capacitors.Use of even one thyristor turn off capable switch, however, allowsadjustment of the valley fill minimum voltage to extend the conductionangle which can be useful especially during phase control dimming.

Referring now to FIG. 3, a switching matrix 30 is shown using a valleyfill PFC circuit 32 with switches G1-G11 added. The PFC circuit 39 mayhave a AC input 34, a capacitive element 36 coupled in parallel to theAC input 34, a diode bridge rectifier 32 coupled to the AC input 34 andcapacitive element 36, and a pair of capacitive elements 38 and 40coupled to the diode bridge rectifier 32 and negative terminal of ACinput 34. Capacitor 36 compensates the fundamental reactive power andabsorbs the harmonic distortion power to yield higher power factor andlow total harmonic distortion. Capacitive elements 38 and 40 increasethe conduction time of the input current by providing an alternate pathfor input current to flow into the circuit before the input linevoltages increases above the valley fill voltage reducing currentdistortion. As in the previous embodiments, the switches G1-G11 may beturn off thyristors such as Gate Turn Off (GTO) or Mos-ControlledThyristor (MCT) transistors (or combinations thereof in on/off triacform). It is possible to utilize none of the shown MCT-GTO or turn offTRIAC switches G-G11 in the valley fill PFC scheme (back to back GTO orMCT to allow bidirectional conduction) or a limited combination and thebenefits of doing so are easily understood by those skilled in the art.Specifically, increasing the conduction angle for charging anddischarging as well as allowing re-distribution of the capacitor for useas an offline charge pump.

Referring now to FIG. 3A, operation operating waveforms of the switchingmatrix 30 is shown. The upper waveform is the input voltage and theoutput voltage except that Vo or Voa shows the valley fill voltage whichdiffers from the rectified input voltage during the valleys. The lowerwaveform shows the input current from the AC input 34. The improvedpower factor and Total Harmonic Distortion (THD) is evident as the inputcurrent I follows the in AC half wave far better than would aconventional peak charging capacitor.

Before t1 the load, LEDs 12, is being entirely supplied by the valleyfill capacitors C1 and/or C6 (if G11 closed) or C5 if G7 is closed aswell with G10 closed. During t1-t2 the input voltage exceeds the valleyfill capacitance and starts charging C1 and supplying the load, then asthe voltage rises we close G11 and open G10 to charge capacitors C1+C6as well as the load. During t2-t2a we close G1 and G8 which charges somecombination of C1+C5+C6 or C1+C2+C6 depending on which is discharged themost and for some period in parallel. From t2a-t3 we close G012 and G6and some combination of the upper three capacitors (C1-C3) and C6 or thelower three capacitors (C4-C6) and C1 are charged. Charge balancing willbasically ensure that all possible conduction paths displace to maximizethe relative voltage across the capacitors against their size in acapacitor divider. Note that if the impedance of the switches is too lowthen resistors may have to be added in series with the diodes tolengthen the conduction time. Also note that fewer switches may be usedbut if even a single switch is used then the valley fill voltage may belowered improving the conduction angle.

From t3-t4 the capacitors C1-C6 (all the capacitors) will charge and theload will be fed directly until peak voltage is reached after which theoutput will still be fed by a combination of the capacitors C1-C6 andthe load since the capacitors C1-C6 are sized to minimize the valleyfill voltage. From t4 to t4a this will continue as it will from t4-t5and t5-t6. After t6 the voltage is smaller than the valley fill voltageand the valley fill capacitors will provide all of the output currentwhile nothing will flow from the input. Improving the input currentdrawn from the AC line during this time requires a load across thesupply independent of the valley fill and load as shown in FIG. 3 36.

The result of splitting up the capacitance this way is an extension ofthe conduction angle. The switches allow utilization of 1-3 threecapacitors on the upper and lower portions which allow adjustment of thevalley fill voltage if desired. Additionally, it may be useful to simplyutilize fewer capacitors or to use a single capacitor and pin out itsplates so that the result looks like multiple capacitors.

If phase control dimming is used as shown in FIG. 3B, then thecapacitors C1-C6 may be rearranged in a parallel combination or seriesparallel combination depending upon the input voltage to keep thecircuit alive during the dead times from t6 to t1 in FIG. 3A. Thisenergy can also be replenished by switching from parallel to a parallelseries combination to charge the capacitors with a low input voltage butstill supply enough voltage to maintain the minimum system voltage (suchas for the control IC) in an offline charge pump type scheme (higherfrequency than line voltage rearrangements of capacitors to conform tothe input voltage during part of a cycle and to an output voltage duringanother portion of the higher frequency cycle). This can drive the loadas well or alternatively may be used to keep the control circuitry aliveif the conduction angle becomes very small. Either way the use of phasecontrol dimming is facilitated through the use of these switches G1-G11due to the ability to re-arrange the capacitors in series and parallelcombinations conforming the input voltage and the output voltage desiredat low dimming levels or as a keep alive.

Referring to FIG. 4A-4B, an example of a novel capacitor constructionfor the capacitors C1-C6 of the previous embodiment is shown. Thecapacitor construction takes the multiply folded plates in standardcapacitors and makes them available for connection in either valley fillPFC combination disclosed above. Alternatively the same construction maybe used to create the offline capacitor as shown in FIG. 5. For exampleif all of the capacitors (C1-C6 FIG. 3) are connected in parallel duringpart of the cycle and then connected to an output capacitor and/or loadduring another portion of the cycle, then an arbitrary voltage may becreated by pumping from any part of the AC input line to a desiredoutput voltage. Not only does this facilitate a voltage mode offlinecharge pump but with proper selection of the intermediate voltage itallows a phase control signal to be pumped to an intermediate voltage asshown in FIG. 6. Rather than relying on a flickering 120 Hz signal, thefaster charge pump rate may control a duty cycle such that the systemonly connects to the load using a duty cycle correlating to a linearizedreplica of the phase control signal, as a fraction of the overall halfwave or other such control function, but at higher frequency which isnot detectable by the eye.

There are a variety of methods translating a phase control signal to aduty cycle, including a direct linear representation which is non-idealdue to eye sensitivity as well as the properties of a sine wave. Saidtranslation transfer functions may utilize the triac setting fromprevious cycles to assume a given triac setting such that newcombinations of capacitors may be used to store energy to optimize thetransfer function as described above or to store maximal energy to keepthe control circuitry alive for very small or vanishing phase angles.

FIG. 7 and FIG. 7A show a vertical sinker structure for an n-MCT. FIG. 7shows a vertical arrangement with the substrate being the anode. Thisarrangement is useable for the common terminal array discussed above,however, for full switching of either the offline charge pumpconfiguration or the more complex LED switching arrangements (or acombination of the two) the MCT needs to be isolated. These structuresmay be isolated by inserting sinkers utilizing isoup and isodown asshown in FIG. 7A and FIG. 7D. FIG. 7A shows this arrangement and FIG. 7Dshows the sinker inserted into the structure. This arrangement bringsthe buried layer or anode terminal up to the surface. By separating theMCTs subcells as shown in FIG. 7D (another subcell is continued to theright without the long p− terminator again and again with a finalsubcell including a mirror image of the FIG. 7 cell including the p−tapered terminator and associated termination elements) it is possibleto create multiple isolated MCTs on the same substrate with separatedanode, cathode and gate terminals which has not been done before.

The operation of the MCT is easily understood by considering the MOSFETsformed by the n-channel n/p+/n structure in the area to the left of then region on the right side and the p+/n/p p-channel arrangement underthe BPSG/TiSi/SiO2 stacks. The TiSi are the gates. When the gate ispositive, the n-channel will inject carriers into the n drift region(n−) to trigger the n/p+/n−/n/p+ scr structures while if the gatevoltage is pulled negative then the p-channel will effectively short thebase-emitter voltage of the npn device in the equivalent circuit of abipolar latch. Control of the drift region, gold doping and irradiationto create sites for recombination can increase the rate of turn off thedevices.

FIG. 7B shows how the construction could be rotated to produce a cellwhich can be repeated to create a large power device.

FIG. 7D can also be used to illustrate that subcells within the MCT maybe coupled to a controller responding to a control signal, such that thegates formed by the Ti—Si areas turn on or off in succession in time ortheir gates are charged or discharged at different rates, to control therate of turn on and turn off of the MCT. It is important, however, toensure that the current through the cells which are on does not growexcessive as they will thermally run away. By ensuring that none of thecells runs away at too fast a pace relative to one another, a controllermay use the turn on/turn off capability of the MCT injecting mechanismto control the spreading of the turn on or off of subcells to create aquasi-linear device. This is useful as it would be possible to turn onor off the device or modulate the current in a way more like a MOSFET orIGBT or alternatively to turn on only a portion of the device to reduceswitching losses.

FIG. 8 illustrates a driver 80 for the MCT, GTO or linear/controlledturn on type devices described above. Multiple drivers are illustratedin this drawing and would likely not be combined in a realimplementation (to the left a scr current driver is connected), to theright different time or charge rate staggered high impedance gate turnon mechanisms are shown to control turn on of different subcellelements). Those skilled in the art would separate these methods. In allcases a level shift 82 with cascodes is used to protect the gates of thehigh voltage MOSFETs. Resistors (rectangles) may be used to degeneratethe low side switches to change the driver switch rate/current throughthe capacitors to current driven devices or may be left out. Inaddition, time constant or size variations may be used to controlmultiple mirror elements turning on different subcells similar to 7D.The upper cascodes connected to the gates of the high voltage p-channellevel shifter devices cascode the gates of the level shift devicesthemselves while the p-cascodes below the level shift crisscrossconnection to protect the gates of the devices being driven. Similarlythe n-channel cascodes protect the low voltage devices connected to theinverter and control terminal at the bottom. This scheme can be extendedutilizing differently sized cascode mirrors in parallel to control theturn on and turn off schemes to control the current rise and fall inconformance with a control signal such as the MCT gate voltage so thatthe devices operate more like MOSFETs or IGBTs (utilizing the subcellsdescribed above). For example with wide swing cascode mirror elements ofdifferent sizes, the mirrors may be setup for the different devices suchthat the current charging the distributed gates may be fanned outdifferently to said subcells to control said turn on and off rates andfurther may be coupled with feedback to said voltage measurementcircuits of the individual cells to ensure no hotspots occur or tocreate constant current operation. Alternatively, RC time constants maybe distributed between the mirrors as shown (CA or CB) to control turnon or turn off rates. Ie. if differently sized RCs are coupled to eachof the mirrored output devices which are in turn connected to thedistributed gates of the turn off thyristors then a linear in time turnon or turn off may be accomplished allowing the MCT to more closelyresemble a MOSFET or IGBT with a linear region (which can help reduceringing and eliminate snubbers). Both the time constant altered cellturn on, or current staggered turn on to vary the rate of turn on andoff of the cells, or a combination, is a means by which to control theplasma spreading or current turn on rate of the devices and produce aquasi-linear response. Those skilled in the art will understand that thelow side needs to be replicated for turn off even though only the uppercascade mirror elements are explicitly drawn.

Utilizing capacitors coupled to GTOs allows the driver configuration inFIG. 8 to be utilized for current triggered devices where the size ofthe switch devices in the level shift, degeneration of the switchdevices, size of coupling capacitors or tunable/controllable capabilityof any of these elements may be used to control the dv/dt such that thetrigger current may be tailored for said GTOs.

FIG. 8 a illustrates the concept of a turn off TRIAC utilizing gatedturn off thyristors to control a bidirectional current.

Referring to FIG. 9, the benefits in current density of an MCT vs. othertypes of devices is shown. FIG. 9 illustrates that MCTs have a highercurrent density which translates into less silicon. This differs fromconventional direct drive means which generally utilize external MOSFETsto short groups of LEDs during different segments of AC waveform. Simplyutilizing these types of devices, however, may not be enough as it maybe necessary to combine them on a single substrate while simultaneouslyisolating to make them useful. Isolated arrays of these types ofthyristors have not been taught before.

FIG. 10 illustrates operation of the offline charge pump wherecapacitors are arrayed from all parallel to series-parallel to fullyseries operation in conformance with the magnitude of the AC inputvoltage, but re-configured to meet an output voltage conforming to thatrequired by the load and/or an output capacitor at a frequency muchhigher than the frequency of the offline signal.

FIG. 11 illustrates some applications in which an offline charge pumpmight be used and the advantages that would accrue.

While the invention has been particularly shown and described withreference to the preferred embodiment thereof, it will be understood bythose skilled in the art that the foregoing and other changes in form,and details may be made therein without departing from the spirit andscope of the invention.

What is claimed is:
 1. A Light Emitting Diode (LED) driving device fordriving a plurality of LEDs comprising: a switching matrix utilizing aplurality of at least one of a turn off thyristors or turn off triacscoupled to the plurality of LEDs; a controller coupled to the switchingmatrix responsive to a voltage of a rectified AC halfwave, whereincombinations of the plurality of LEDs are altered to ensure a maximumoperating voltage of the plurality of LEDs is not exceeded; and acurrent limiting device coupled to the combinations of the plurality LEDto regulate current.
 2. A Light Emitting Diode (LED) driving device fordriving a plurality of LEDs in accordance with claim 1 furthercomprising a valley fill power factor correction (PFC) circuit coupledto the switching matrix, to draw current in proportionality with therectified AC half wave.
 3. A Light Emitting Diode (LED) driving devicefor driving a plurality of LEDs in accordance with claim 2 wherein thePFC circuit comprises: a switched capacitor array having a plurality ofcapacitors, wherein the switched capacitor array uses at least one ofturn off thyristors or parallel reverse combinations as switchingelements to create a turn off triac connected to at least two of theplurality of capacitors; and a switched capacitor array controllercoupled to the switched capacitor array to adjust a voltage of thevalley fill PFC circuit by activating and deactivating combinations ofthe switching elements.
 4. A Light Emitting Diode (LED) driving devicefor driving a plurality of LEDs in accordance with claim 3 furthercomprising: a transfer function coupled to the switched capacitor arraycontroller for translating a phase angle to a desired dimming transferfunction; wherein the switching elements of the switched capacitor arrayallow switching parallel combinations of capacitors in addition tovalley fill PFC combinations wherein parallel, parallel-series, orpurely series combinations may be assembled; wherein the switchedcapacitor array controller is responsive to phase control dimming suchthat the plurality of capacitors are arranged to store a maximum energyfor an expected phase angle without exceeding their voltage capabilityas determined in one or more previous half wave cycles.
 5. A LightEmitting Diode (LED) driving device for driving a plurality of LEDs inaccordance with claim 3 wherein the desired dimming transfer function isone of linear, geometric or a non-linear function correlated to visualacuity to optimize a phase control signal.
 6. A Light Emitting Diode(LED) driving device for driving a plurality of LEDs in accordance withclaim 4 wherein the plurality of capacitors are utilized to power theswitched capacitor array control circuit for the chopped portion of therectified AC half wave;
 7. An offline charge pump device comprising: aswitched capacitor array having a plurality of capacitors using at leastone of turn off thyristors or parallel reverse combinations as switchesto create a turn off TRIAC connecting at last two of the plurality ofcapacitors; a controller device operating at a frequency higher than anAC rectified half wave coupled to the switched capacitor arrayresponsive to a voltage of the rectified AC half wave, the controllerdevice forming capacitor combinations from the plurality of capacitorssuch that the capacitor combinations do not exceed their individualmaximum voltage ratings during a first part of a frequency cycle, thecontroller device rearranging the capacitor combination resulting in adesired output voltage during a second part of the frequency cycle; and;at least one of coupling devices for connecting the plurality ofcapacitors by the turn off thyristors to the voltage of the AC half waveduring the first part of the frequency cycle and then to an outputduring the second part of the frequency cycle.
 15. A capacitor devicecomprising: a plurality of plate members, wherein the plurality of platemembers are separately segmented out to create individually accessiblecapacitors, wherein each capacitor has a lower voltage tolerance thanacross the entire series combination.
 16. A Light Emitting Diode (LED)driving device for driving a plurality of LEDs in accordance with claim3 further comprising a plurality of plate members, wherein the pluralityof plate members are separately segmented out to form a plurality ofpinned out segments, the plurality of pinned out segments forming theplurality of capacitors.
 17. An offline charge pump in accordance withclaim 7, further comprising a plurality of plate members, wherein theplurality of plate members are separately segmented out to form aplurality of pinned out segments, the plurality of pinned out segmentsforming the plurality of capacitors.
 18. A vertical thyristor arraycomprising: an array of at least one or more of MCT or GTO thyristors;wherein the plurality of one of a MCT or GTO thyristors are formed on acommon substrate, with one of a common anode or cathode connected to thecommon substrate, for all plurality of one or more of a MCT or GTOthyristors in said array.
 19. A thyristor array formed on a commonsubstrate comprising: a plurality of isolated vertical structure turnoff thyristors, wherein each of the turn off thyristor is one of a MCT,GTO, or turn off TRIACs; wherein each of the plurality of verticallystructure turn off thyristors has isolated terminals and is isolatedfrom the other turn off thyristors;
 20. An (n-MCT) MOS ControlledThyristor comprising: a p+ buried layer on a bulk silicon substrate; adoped n region formed above said p+ region; a lightly doped n-epivertical drift region for dropping high voltage from anode to cathode;(optional) recombination acceleration means within said n-epi region toimprove switching performance; A ptub created above said n− driftregion; a group of doped n-tubs created within said p-tub; at least onep+ region formed within each of said n-tub regions; a gate coupling saidp tub to said p+ region across said n-tub surface to form a MOSFET forshorting an equivalent npn base emitter junction within the equivalentcircuit from the thyristor latch to turn it off; one or more n-tub aboven− regions between said ptubs; a gate coupling n-tubs within said p-tubregion to said n region above said n-epi drift region through said p-tubregion for the purpose of injecting carriers into the thyristor latch toturn it on; a metal connection to couple said p+ and ntub regions to afirst terminal to create a cathode; metal-Ti—Si connections to couplesaid gates to one or more gate terminals; BPSG isolation around saidTi—Si gates; a p+ sinker to contact said p+ buried layer forming theanode; and a metal connection to couple said p+ sinker to a thirdterminal to create an anode.
 21. A MOS Controlled Thyristor inaccordance with claim 20 further comprising a nitride passivation layerformed on a top surface, said gate and cathode and anode terminalsexposed.
 22. A (p-MCT) MOS controlled thyristor created by utilizing thecomplement doping in 20 such that n type regions are replaced with ptype regions;
 23. A MOS controlled thyristor in accordance with claim 20further comprising an n isolation region or a dielectric isolationregion between groups of thyristor cells to allow creation of multipleisolated thyristor devices on a single substrate;
 24. A MOS controlledthyristor in accordance with claim 23 further comprising a thinamorphous silicon layer and nitride passivation layer with anode,cathode and gate terminals exposed.
 25. A Light Emitting Diode (LED)driving device for driving a plurality of LEDs in accordance with claim1 wherein the current limiting device is one of a transconductor, alinear turn off thyristor, or a resistor.
 26. A driving circuit for aMCT comprising: a cascoded level shift device, wherein a maximum gatevoltage for said MCT is protected by cascoded devices within the levelshift structure.
 27. A current controlled turn off thyristor controlnode driving scheme comprising: a capacitively coupled level shiftdevice, wherein a maximum voltage on an integrated capacitor isprotected by cascode devices.
 28. A turn off triac driver device where apgto is in parallel with an ngto connected anti-parallel to allowbi-directional current flow and interruption comprising: a level shiftstructure with cascodes to limit the voltage switch magnitude to protectlevel shift gates as well as limit the voltage change across eachcoupling capacitor; and two coupling capacitors coupled to each of thelevel shift outputs such that a controlled charge may be injected into aturn off triac back to back gto devices;
 29. A turn off triac driverdevice in accordance with claim 28 further comprising a dv/dt controldevice coupled to said level shift which controls the current magnitudeinto the current control nodes of the turn off thyristors, wherein saiddv/dt control device could be resistors degenerating the lower sideswitches and/or RC combinations coupled to the gates of the mirroredoutputs switches.